Sphalerite is a somewhat common trace mineral in West Virginia coals
filling voids originally present in the peat. In the case shown here,
the minerals sphalerite, pyrite and kaolinite grew within open cavities
in semifusinite ("fossil charcoal") in the Pittsburgh coal. In semifusinite,
the original plant cell walls were carbonized by fire into strong, pure
carbon, remnants of the original cell walls with openings where the cell
contents were located. Dissolved ions in the peat waters precipitated
into various minerals in these voids as the peat formed. Silicon
and aluminum were most abundant and crystallized into very common kaolinite,
Al4(Si4O10)(OH)8, iron and
sulfur formed less common pyrite, FeS2, zinc and sulfur formed
sphalerite, ZnS, and barium and sulfur formed barite,
BaSO4. The sphalerite shown in this SEM
image also contained a significant amount of barium in an unknown association
with the sphalerite. Sphalerite in coal also commonly contains small
amounts of cadmium and is probably the major site of Cd in coals.
Other associations of sphalerite with galena and
in semifusinite have been noted in West Virginia coals.
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